SEOUL North Korea's new and improved ballistic missile shows the country's weapons development is proceeding swiftly despite international pressure, though experts say a fully functional nuclear-tipped deterrent remains a long way off.

The rocket launched on Nov. 29 was a Hwasong-15 intercontinental ballistic missile, North Korea said in a statement released later in the day. The lofted trajectory, which sacrifices range for height, took it to a maximum altitude of 4,475km, the statement said. The Hwasong-14 that the North fired on July 28 reached as high as 3,724km. Pyongyang claims that the new missile can strike anywhere in the U.S.

Experts believe the new missile could travel over 10,000km when fired at a more typical angle. South Korea's National Intelligence Service says the missile is an upgraded version of the Hwasong-14 and the most advanced fired by Pyongyang in its three ICBM launches.

Such rapid development seems due to North Korea's willingness to channel scarce human and economic resources into its nuclear and missile programs. The teams developing these weapons are the best Pyongyang can assemble. Even as officials in the military and the ruling Workers' Party live in fear of leader Kim Jong Un's frequent purges, failures by weapons scientists are said to be tolerated as the cost of progress, creating an environment conducive to success. After the North held its sixth nuclear test in September, Kim rewarded engineers with a banquet in their honor.

Like the bulk of its predecessors, the Hwasong-15 uses liquid-fuel propulsion. This enables fine adjustments to engine output, increasing accuracy. But liquid fuel takes time to load before firing, diminishing combat readiness and making a pending launch easier to detect.

The North's solid-fuel Pukguksong missiles do not have these drawbacks, enabling the element of surprise. Many South Korean experts believe the North will maintain both types in its arsenal, using liquid fuel for ICBMs and solid rockets for shorter-range surface- and submarine-launched missiles.

"Kim Jong Un declared with pride that now we have finally realized the great historic cause of completing the state nuclear force, the cause of building a rocket power," Pyongyang said in a statement after the launch.

But it is unclear whether the country has obtained the technology needed to protect an ICBM's payload when it re-enters Earth's atmosphere. Many experts say that confirming this capability would require testing an ICBM at a normal, rather than a lofted, trajectory, something North Korea has not yet done.